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Show REPORT OF THE CHIEF OF ENGINEERS. 339 CURRENT OBSERVATIONS. Observations for gauging the Colorado River were made at Stone's Ferry, Nov., Camp Mohave, Ariz., and Fort Yuma, Cal. The surface-floats used were (for want of better materials) made from thin boards, obtained from packing and cigar hoses. A piece of sheet-lead was nailed to the under surface to steady the float and bring its upper surface near the surface of the water. A small flag was attached to the upper side by means of a wire about 3 inches long. As but one boat could be obtained at Stone's Ferry and Camp Mohave, a sufficient number of floats were made and allowed to run through without being picked up. At Stone's Ferry the subsurface-float was a box 10 inches square by 14 inches high, open at both ends, and weighted with lead to sink it. This was attached by a cord to a small empty canteen, which served to keep it at a constant depth. To the box was attached a long trail-cord, which was paid out a.s the float left the boat, and by which it was pulled back after making the transits. On account of the rapid current and the resistance offered by the box, it was extremely difficult to draw it back to the boat; hence a large canteen, which was nearly tilled with water, was substituted for the box. This canteen was 9 inches in diameter, aud 3A inches thick. Even this required great exertion in pulling it back to the boat, aud the trail-cord finally broke, allowing the whole arrangement to float down the river. The boat used here was large and unwieldy, extremely difficult to manage in the rapid current. As no anchor could be obtained, a .substitute was used in the shape of a sack filled with stones. This had to be very heavy in order to hold the boat against the strong current, making it very tedious and laborious to handle. A base-line of 260 feet was carefully measured on the south bank and transits placed at the extremities. The times of transit were takeu by a separate observer. The boat was pulled into position and the anchor dropped. It was then located by means of the transits, sounding taken, and at a signal from the observer at the upper transit a surface or subsurface float was sent out from the boat, the time and position of the float at each transit being noted by the observers. As material for surface-floats was scarce, chips were occasionally thrown in and their transits noted. A sufficient number of soundings were taken to determine the cross-section of the river opposite the base-lines, and meander-lines were run aud topographical stations made to furnish material for a complete topographical sketch of the locality. For plotting, the section was divided into divisions of 50 feet each, numbered consecutively from the bane-line. onSKIJVATIONS .\T STOXK's KKRItV, JCEV. The following values were obtained by measurement and computation. The fall of the river was found by leveling to be $.13 feet per mile, or slope = o.utxuo:$=«. Area of section = 57*2^ square feet - a. Width = 4*0 feet = W. Wetted perimeter of section s 4*1.4 =j>. Mean radius = £ = r = ll.?Jfeet B= -f.- N,=".4C»1 ¦"*. I nder the circumstances it was impracticable to take a full set of mid-depth observations ; hence, reliance has to Ik? placed on the results obtained from the surfacc-noats. Sections were only measured between the transit-lines, consequently the formula for the slope cannot be used. The determination <>f the mean from the surface-velocity has been made according to the method indicated in chapter IV, Humphreys and Abbot's Physics aud Hydraulics of the Mississippi River. No correction has been made for wind. The mean velocity as deduced, is r = 3.417 feet, and the discharge, Q ^ ta - 18410.38 cubic feet per second. CIKKKXT OIISKIJVATIOXS AT CAMP MOIIAVE. The method of observation and the character of surface-floats were the same as at ©tone's Ferry. The subsurface-floats used hero consisted of a square tin can with top and bottom covert» removed. This was kept at the required depth by means of a cord attached to a small eork 4loat which carried a small llajj. A trail-van! was attached to pull th« noat back to the boat, after making the transits, as but one boat could be obtained "ear the Post. The base-line was :MM feet long, measured with a compensated steel :?!•*• All the water passed through the section, except a small portion which flows through a shallow channel near the west bank. This had a cross-sectional area of 1' square feet, aud tho water flowing through it a mean velocity of l.'io feet per second. The fall per mile obtained by leveling was. 1/2 feet or * = O.0O0-2J7. for the section at this place, we have the following values: Area of section = a - «*¦" Millar* feet. >Vidth = W = 1110 feet. |